1. Field
The invention has to do with the treatment of oil shale, either in situ or at the surface, with a hot gas for the recovery of valuable constituents from the kerogen content thereof.
2. State of the Art
In my application Ser. No. 785,552 filed Jan. 5, 1959, which was abandoned after an unsuccessful appeal to the Court of Appeals of the District of Columbia from a decision of the District Court for the District of Columbia in the case of Clarence I. Justheim v. David L. Ladd, Commissioner of Patents, 147 U.S.P.Q. 306, it was shown by testimony of Dr. John F. Schairer of the Carnegie Institution, Washington, D.C., that oil shale subjected to 2000.degree. F. in a crucible will fissure extensively and become susceptible to the passage of heat and evolved gases, and other distillation products therethrough. Since Llungstrom U.S. Pat. No. 2,732,195 of Jan. 24, 1956 discloses the use of an electric heater, dropped down a bore hole in an underground oil shale formation to impose a temperature of up to 1000.degree. C. (1836.degree. F.) on the surrounding oil shale, and since tests by Dr. Schairer at 1832.degree. F. showed some fissuring, the court in effect decided that the use of 2000.degree. F. was a mere unpatentable extension of the teaching of the Swedish patent.
Even though the testimony of Dr. Schairer was to the effect that the extent of fissuring at the 2000.degree. F. temperature, was indeed surprising, no one since that time to applicant's knowledge has proposed the use of such a high temperature in the treatment of oil shale, except applicant by his own U.S. Patents, No. 3,598,182 of Aug. 10, 1971, and No. 3,766,982 of Oct. 23, 1973, and Guido O. Grady in his U.S. Pat. No. 3,692,110 of Sept. 19, 1972, which is assigned to Cities Service Oil Company.
Applicant's latter patent, U.S. Pat. No. 3,766,982, teaches the use of an inexpensive hot gaseous fluid, such as air or flue gas, as a super-hot, heat transfer agent to volatilize kerogen and to crack and fissure the oil shale to make it permeable to gas flow therethrough. In accordance with the teaching, the gas (e.g. air) is heated either above or below ground by means of a nuclear reactor, pebble heater, or other suitable device to the 2000.degree. F. temperature and is injected into an underground oil shale formation by means of one or more bore holes extending downwardly from the surface. One or more recovery bore holes are driven into the formation apart from the gas injection bore holes, and a heat front, provided by this super-hot injected gas, migrates from the injection bore holes toward the recovery bore holes through the intervening oil shale, rendering such intervening oil shale pervious to the flow of both the injected gas and of volatilized kerogen resulting from the applied heat. The patent is particularly concerned with at least partial hydrogenation of the kerogen vapors before they are brought to the surface through the recovery bore holes and teaches the injection of hydrogen gas into the path of flow of the vaporized kerogen in the vicinity of such recovery bore holes, whereby at least partially hydrogenated hydrocarbonaceous vapors are withdrawn through said recovery bore holes.
The Grady patent merely mentions a hot zone temperature between about 700.degree. F. and about 2,500.degree. F. in retorting a rubble of broken oil shale in situ in the chimeny created by a nuclear explosive, which chimney is shown packed full of such rubble. Retorting is accomplished by the injection of a "retorting fluid" (a combustion or combustive gas or steam) into the rubble and causing it to filter through the rubble to a production well.